Answer:
David's average speed is 55 mph and Andrew's average speed is 70 mph
Step-by-step explanation:
Let David's speed be s.
Average speed is given as:
speed = distance / time
They both spent the same time, t.
David's speed is:
s = 110 / t
=> t = 110 / s
Andrew travels 15 mph faster than David.
Andrew's speed is:
(15 + s) = 140 / t
=> t = 140 / (15 + s)
Therefore, since they spent the same time:
110 / s = 140 / (15 + s)
Cross multiply:
110(15 + s) = 140s
1650 + 110s = 140s
1650 = 140s - 110s
30s = 1650
s = 1650 / 30
s = 55 mph
Andrew's speed is:
15 + 55 = 70 mph
Therefore, David's average speed is 55 mph and Andrew's average speed is 70 mph.
